The invention relates to a method and a device for controlling a thick matter pump with two feed cylinders which open through front-side openings into a material feed tank and which can be operated in a push-pull manner by means of at least one hydraulic reversing pump and by hydraulic driving cylinders controlled by the reversing pump, with a hydraulically operable tube switch configured inside the material feed tank which is suitable for connection on the intake side alternately to each of the openings of the feed cylinder and which releases the opening of the other feed cylinder, and is suitable for connection on the output side to a delivery pipe, whereby at the end of each feed-cylinder compression stroke, a tube-switch reversing operation is initiated and during the reversing operation the delivery of thick matter is interrupted.
A method for controlling a double-cylinder thick matter pump of this type is known (German Published Patent Application 32 53 576), wherein both the driving cylinders of the feed cylinder as well as the hydraulic actuating elements of the tube switch are pressurized directly by the pressurized oil delivered by the hydraulic reversing pump. Therein, however, 2/2 diverter seated valves are installed in the lines of the main feed cycle leading to the driving cylinders. These 2/2 diverter seated valves, for their part, are controllable by a braking valve. At the end of each compression stroke, an electric end-position signal immediately initiates the reversing action for the reversing pump. To prevent the thick matter material, which had been drawn in previously, from being fed back to the material feed tank, at the moment the reversing pump is switched over, the braking valve is reversed with the result that the 2/2 diverter seated valves are brought into their closed position, so that the pressurized media cannot flow from the reversing pump into the lines leading to the driving cylinders. At the same time, a sufficient pressure builds up in the specific high-pressure-media line leading to the actuating element to switch through the hydraulic actuating elements of the tube switch by means of a reversing valve. The switching of the reversing valve is delayed by means of a low-pass filter until the tube switch is switched over. After that, the 2/2 diverter seated valves are again opened for both flow-through directions. It can happen, however, primarily when thick matter with coarse components or when hardened thick matter, such as concrete, is conveyed, that the tube switch jams in the course of the switch-over operation and therefore does not switch through completely. Since the seated valves configured in the main circuit open automatically after the expiration of the delay time set at the low-pass filter, the result is that the material drawn in previously by a feed cylinder is fed back unintentionally to the material feed tank. When this backlash repeats itself due to permanent jams, rapid wear and tear or even destruction can result in the tube-switch area. Furthermore, in the case of the known circuit configuration, it has proven disadvantageous that seated valves, whose size must be adapted to the main oil flow, are configured in the main circuit leading from the reversing pump to the driving cylinders. Therefore, it is not possible to increase the output volume by switching in additional, parallel-connected reversing pumps without simultaneously exchanging the diverter seated valves in the main circuit, if these had not been oversized from the start.
Starting from here, the object of the invention is to develop a method and a device for controlling a thick matter pump of the type indicated at the outset, with which a hydraulic sequencing control of the driving cylinders and of the tube switch is possible without having to configure any valves or fittings in the main oil circuit.